Appendix C - Stormwater Management Plan

TfA Project Group Pty Ltd                                                                           Stormwater Management Plan
                                                                                                         Development Application


   Where:
   Qy = peak flow rate (m3/s) for average recurrence interval (ARI) of ‘y’ years
   Cy = coefficient of discharge (dimensionless) for ARI of ‘y’ years
   A = area of catchment (ha)
   tIy = average rainfall intensity (mm/h) for a design duration of ‘t’ hours and an ARI of ‘y’ years.


   t = the nominal design storm duration as defined by the time of concentration (tc).
   The value of 2.78 x 10-3 (or 1/360) is a conversion factor to suit the units used.


   6.2.2      Catchments
   The existing catchment boundary has been maintained in the post development scenario. Pre and post-
   development catchment information is tabulated in Table 4 below.


   Table 4: Catchment details

      Pre-development              Pre-development          Post-development          Post-development
           Area (Ha)              fraction impervious            Area (Ha)           fraction impervious
              0.24                         0.0                      0.24                    0.68


   6.2.3      Time of concentration
   The time of concentration of the pre-development scenario was calculated using the Friend’s equation for
   overland sheet flow and figure 4.09 and 4.10 of the Queensland Urban Drainage Manual (QUDM 2007). The
   equation is shown below:


                        tc = (107.n .L0.333) / S0.2                                             (QUDM 2007: Equation 4.06)


   Where:
   tc = overland sheet flow travel time (min)
   L = overland sheet flow path length (m)
   S = slope of surface (%)
   The value ‘107’ is a conversion factor to suit the units used.


   The time of concentration for post-development scenarios was determined using the above equation 4.06 with a
   minimum of 6 minutes as instructed in the Planning Scheme Policy 5 - Noosa Council. Table 5 below shows the
   times of concentration used in the water quantity assessment.


   Table 5: Times of concentration for the catchment

                            Catchment                                                Time of concentration
                     Pre-development                                                        10.00
                     Post-development                                                        6.00


   6.2.4      Coefficient of Discharge
   From Table 4.05.3(a) and 4.05(b)of QUDM, a one hour rainfall intensity for a 1 in 10 year ARI (1I10) of 72.3 mm/hr
   and fraction impervious fi of 0.0 has a C10 value for the pre-development catchment of 0.70. The post-
   development C10 value is 0.84. Table 6 below shows the Fy factor used to calculate the Cy value for each ARI.


                            123 Eumundi Road (Cnr Walter Hay Drive), Noosaville QLD 4566                                      Page 5